1. Field of the Invention
This invention relates to controllers for switch machines and, more particularly, to electronic controllers for railway switch machines or for transit and/or railway related vital proximity detection applications.
2. Background Information
A railway switch machine is used to divert a train from one track to, another track. In many cases, the switch machine is remotely operated and, thus, an operator cannot see the machine. Consequently, the status of the machine (e.g., points detected and mechanically locked for either a straight-through or turn-out move) is provided by electrical circuits that, in turn, are interlocked with signals governing movement of the trains. According to typical convention, the term Normal (N) is employed for a straight-through move and the term Reverse (R) is employed for a turn-out move.
Historically, indication circuits for switch machines were implemented with cam operated or other types of mechanical switches within the machine. In some cases, the indication contacts of one machine are electrically connected in series with other machines. All interconnected machines must prove that their points are closed and mechanically locked before railroad signals are cleared, in order to permit movement of associated trains.
Motor control is also provided by mechanical switches. Basically, the motor rotates in opposite directions for Normal and Reverse. Rotary motion of the motor is converted to linear motion within the machine to move and lock the points. If the motor is being driven Normal, then contacts within the machine open the circuit path that would, otherwise, permit continued movement in that direction when the limit of intended motion is reached. However, a path is maintained that permits movement in the Reverse direction. In between the extreme positions, both current paths are closed for movement of the motor in either direction.
It is known to assign Right Hand Points Closed (RHPC) or Left Hand Points Closed (LHPC) to Normal by orientation of cam operated switches.
With mechanical controllers, a battery voltage is fed from the wayside case to contacts of a first switch machine. Then, if those contacts are closed, the battery voltage is fed on to the next machine, and so on. If all the contacts in the, series string are closed, then the voltage fed back to the wayside case proves all switch machines are in correspondence, which is a condition necessary to clear signals.
U.S. Pat. No. 5,806,809 discloses inductive proximity sensors, which are employed to detect the position for a railroad switch machine.
It is a known practice with mechanical machines to interrupt an indication output when hand operation of the machine is initiated.
U.S. Pat. No. Nos. 5,116,006; and 5,192,038 disclose safety detectors for a railroad switch point.
U.S. Pat. No. 5,504,405 discloses a switch machine controller with a fail safe mechanism.
U.S. Pat. No. 5,142,235 discloses a detection system in which a proximity switch and a controller are connected by a pair of wires. A small leakage current exists when the sensor is in a normal off state, and another electric current flows in a normal on state. One side of the proximity switch is electrically connected to a power source by one wire, while the other side is electrically connected to ground by the series combination of the other wire and a resistor. A set of four comparators receives four different reference voltages from five series resistors between the power source and ground. These comparators also receive a divider voltage, which is formed by the proximity switch and the resistor. A logic circuit receives the outputs of the four comparators and determines one of five states: (1) short circuit; (2) normal on; (3) unstable; (4) normal off; and (5) line breakage.
U.S. Pat. No. 5,218,298 discloses a magnetic-field monitor including a Hall sensor having two terminals. The sensor is energized by applying a DC voltage across these terminals. A Hall-sensor signal decoder circuit includes a current mirror circuit having transistors, a saturating high-current protection circuit, a voltage divider circuit including series resistors, and three comparators having reference voltages and outputs, respectively. The signal decoder circuit is electrically connected to the Hall sensor such that a current, Id, which is proportional to the Hall sensor current, Is, flows through the divider resistors. The three binary output signals from the comparators constitute a binary indication of whether a short circuit fault, an open circuit fault, or a high or low ambient magnetic field exists at the sensor.
U.S. Pat. No. 4,574,266 discloses a microcomputer controlled monitoring system including a load detector circuit for detecting an electrical open, shorted or operative condition of an electrical load.
U.S. Pat. No. 5,986,549 discloses a resonant sensor system, which may be employed in an object proximity-sensing mode.
U.S. Pat. No. 6,062,514 discloses a railway switch circuit controller, which employs eddy current proximity sensors to determine when a railway switch is in a normal or a reverse position.
U.S. Pat. No. 5,418,453 discloses diagnostics for variable reluctance wheel speed sensors. These diagnostics detect sensor and harness short and open circuits by comparing signals to programmable thresholds and time limits.
U.S. Pat. No. 5,868,360 discloses a vehicle presence detection system. If a search coil is shorted, then the voltage change at a subsequent operational amplifier will be absent or greatly attenuated. If, on the other hand, the coil is open, then one operational amplifier saturates at its upper voltage limit and another operational amplifier saturates at its lower voltage limit. In turn, the disappearance of a carrier during self-test, thus, indicates an open search coil.
U.S. Pat. No. 5,844,411 discloses a diagnostic circuit for detecting fault conditions in a Hall effect digital gear tooth sensor in a vehicle""s four-wheel drive system. The diagnostic circuit is designed such that a fault, whether it be a short circuit or an open circuit, causes the voltage at specific points to fall below or rise above predetermined values. When a window comparator circuit detects a voltage level outside the specific range of values, it provides a signal to a system controller. The system controller then sends a signal to an indicator, which alerts the driver of the vehicle that a problem exists.
U.S. Pat. No. 5,247,245 discloses a test apparatus for different electrical sensors. A magnetic sensor is operating properly if a red LED indicator flashes on whenever the sensor is passed near ferrous metal or a magnet. The sensor is defective or inoperative if, instead, the red LED indicator never comes on meaning that an open circuit condition exists in the sensor. If the indicator always stays on, then this means that the sensor is shorted out. A proximity (or Hall Effect) sensor is operating properly if the red LED indicator changes its condition whenever placed next to the proper size magnet, regardless of whether the LED indicator was on or off before being placed next to the magnet.
There remains the substantial need (e.g., personnel safety, equipment safety) to provide a fail-safe controller for a switch machine.
This need and others are met by the present invention in which enhanced safety is provided in a controller for a switch machine by distinguishing ON and OFF sensor states from indeterminate sensor states for two sensors of both point detecting means and lock detecting means.
In accordance with the invention, a controller for a switch machine comprises: point detecting means for detecting when an indication rod is in a first point position and when the indication rod is in a second point position, the point detecting means including a first proximity sensor for detecting a target of the indication rod when the indication rod is in the first point position and a second proximity sensor for detecting the target of the indication rod when the indication rod is in the second point position, the first proximity sensor generating a first point detection signal and the second proximity sensor generating a second point detection signal, the first point detection signal having a value within a first predetermined range of values when the indication rod is in the first point position and having a value within a second predetermined range of values, which is different from the first predetermined range of values, when the indication rod is not in the first point position, the second point detection signal having a value within a third predetermined range of values when the indication rod is in the second point position and having a value within a fourth predetermined range of values, which is different from the third predetermined range of values, when the indication rod is not in the second point position; lock detecting means for detecting when a lock box is in a first lock position and when the lock box is in a second lock position, the lock detecting means including a first proximity sensor for detecting a target of the lock box when the lock box is in the first lock position and a second proximity sensor for detecting the target of the lock box when the lock box is in the second lock position, the first proximity sensor of the lock detecting means generating a first lock detection signal and the second proximity sensor of the lock detecting means generating a second lock detection signal, the first lock detection signal having a value within a first predetermined range of values when the lock box is in the first lock position and having a value within a second predetermined range of values, which is different from the first predetermined range of values of the first lock detection signal, when the lock box is not in the first lock position, the second lock detection signal having a value within a third predetermined range of values when the lock box is in the second lock position and having a value within a fourth predetermined range of values, which is different from the third predetermined range of values of the second lock detection signal, when the lock box is not in the second lock position; means for processing point detection information from the first and second point detection signals and the first and second lock detection signals to provide a first output and a second output, the means for processing enabling the first output when the first point detection signal has a value within the first predetermined range of values thereof, the second point detection signal has a value within the third predetermined ranges of values thereof, the first lock detection signal has a value within the first predetermined ranges of values thereof, and the second lock detection signal has a value within the third predetermined ranges of values thereof, the means for processing enabling the second output when the first point detection signal has a value within the second predetermined range of values thereof, the second point detection signal has a value within the fourth predetermined ranges of values thereof, the first lock detection signal has a value within the second predetermined ranges of values thereof, and the second lock detection signal has a value within the fourth predetermined ranges of values thereof, the means for processing disabling the first and second outputs when any of the first point detection signal has a value different than the first and second predetermined ranges of values thereof, the second point detection signal has a value different than the third and fourth predetermined ranges of values thereof, the first lock detection signal has a value different than the first and second predetermined ranges of values thereof, and the second lock detection signal has a value different than the third and fourth predetermined ranges of values thereof; and means for indicating the first and second outputs.